The Institute of Electrical and Electronics Engineers (IEEE) 802.16m system may support both a Frequency Division Duplexing (FDD) scheme, which includes a Half-Frequency Division Duplexing (H-FDD) Mobile Station (MS) operation scheme, and a Time Division Duplexing (TDD) scheme. The IEEE 802.16m system uses Orthogonal Frequency Division Multiplexing Access (OFDMA) as a multiple access scheme in downlink (DL) and uplink (UL).
The following is a brief description of a frame structure of an IEEE 802.16m system.
FIG. 1 illustrates a basic frame structure in the IEEE 802.16m system.
As shown in FIG. 1, each 20 ms superframe is divided into four 4 ms radio frames of the same size and starts from a superframe header (SFH). When the IEEE 802.16m system has a channel bandwidth of one of 5 MHz, 10 MHz, and 20 MHz, each 5 ms radio frame may consist of 8 subframes. Each subframe may be allocated for downlink or uplink transmission. A 1st-type subframe may be defined as a subframe including 6 OFDMA symbols, a 2nd-type subframe may be defined as a subframe including 7 OFDMA symbols, and a 3rd-type subframe may be defined as a subframe including 5 OFDMA symbols.
The basic frame structure may be applied to both the FDD scheme, including the H-FDD MS operation scheme, and the TDD scheme. In a TDD system, each radio frame has two switching points. The switching points may be defined according to change of the directionality from downlink to uplink or from uplink to downlink.
An H-FDD Mobile Station (MS) may be included in the FDD system. From the viewpoint of the H-FDD MS, the frame structure is similar to the TDD frame structure. However, downlink and uplink transmission are performed in 2 individual frequency bands. Transmission gaps between downlink and uplink (or between uplink and downlink) are required for switching between transmission and reception circuits.
FIG. 2 illustrates an example of an FDD frame structure of a 5 MHz, 10 MHz, or 20 MHz channel bandwidth, whose CP length is ⅛ of an effective symbol length.
As shown in FIG. 2, a Base Station (BS) that supports the FDD scheme can support both a half-Duplexing MS and a full-Duplexing MS that operate with the same RF carrier. The MS that supports the FDD scheme needs to use one of the H-FDD or FDD scheme. All subframes may be used for downlink and uplink transmission. Downlink and uplink transmission may be discriminated in the frequency domain. One superframe may be divided into 4 frames and one frame may consist of 8 subframes.
As described above, the IEEE 802.16m system needs to support both a Half-Frequency Division Duplexing (H-FDD) scheme and a Full-Frequency Division Duplexing (F-FDD) scheme and also needs to support an MS that uses the legacy system. However, a frame structure that supports both an MS that uses the legacy system and an MS that uses the advanced system has not been suggested until now. In addition, no studies have been conducted on a frame structure that can support not only 2 or more wireless communication schemes but also an MS that uses the H-FDD frame structure. Accordingly, there is a need to study a frame structure that can support both the legacy MS and an MS that uses the H-FDD frame structure.